Method for producing a fermented dairy product

ABSTRACT

The present invention relates to a method for producing a fermented dairy product including the use of an oxidase for the conversion of lactose to lactobionic acid. Moreover, it refers to a method for affecting firmness and/or sourness of a fermented dairy product. Hereby is produced a fermented dairy product having improved functional and/or organoleptic properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 10/282,380,filed Oct. 29, 2002, which claims, under 35 U.S.C. 119, priority ofDanish application nos. PA 2001 01632, filed on Nov. 2, 2001, PA 200101864, filed on Dec. 13, 2001 and claims the benefit of U.S. provisionalapplication Nos. 60/333,358, filed on Nov. 26, 2001 and 60/341,175,filed on Dec. 13, 2001 the contents of which are fully incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a method for producing a fermenteddairy product including the use of an oxidase for the conversion oflactose to lactobionic acid.

BACKGROUND OF THE INVENTION

In the production of fermented dairy products, such as yoghurt, creamcheese, cottage cheese etc. functional and/or organoleptic properties,as well as nutritional value are of importance. Among the organolepticproperties sourness, firmness and mouthfeel of the dairy product is ofgreat importance for customer acceptance. Moreover, there aredifferences in customer acceptance based on national and culturaldifferences, which fact requires these properties to be adjustable.

Many efforts have been exercised in order to generate dairy products ofnutritional value and with improved functional and/or organolepticproperties, including acidified, edible gels on milk basis. A typicalexample of such products is desserts, especially yoghurt and curd. Inorder to prepare such products of satisfactory quality, it is todaynecessary to ferment dairy ingredients (whole or low fat milk, skimmilk, condensed milk, and dried skim milk) using bacterial cultures.Some of these may be indigenous to milk or introduced during processing.Fermentation not only reduces pH of the milk, but also results in thesmooth, viscous liquid or soft curd characteristic of yoghurts.Stabilizers and sweeteners are often added during processing to modifytexture and/or prevent syneresis as well as reduce intensity of the tartor sour flavor (Kosikowski & Mistry: Cheese and fermented milkproducts). For example, Swiss-style yoghurt uses large amounts up to0.75% of stabilizer to obtain products of high viscosity.

In many fermented dairy products, particularly yoghurt products,firmness and sourness are of great importance. E.g. yoghurt is asoft-textured product where texture and sourness are of specificimportance for the final product to be used, eaten as such, or used in aprepared ready-to-eat form. Metabolic activity of the bacterial culturesgenerate volatile flavor compounds such as acetic acid, diacetyl, andacetaldehyde which coupled with the acidity contribute to the uniquesour or tart flavor characteristic of yoghurts. However, the tartness orsourness may be too intense and may need to be reduced by addingsweeteners. Another unique characteristic of yoghurt is its viscosityand smooth mouthfeel. The occurrence of syneresis during storagereleases whey from the smooth gel matrix resulting in significantchanges in texture. Hence the addition of stabilizers to prevent orcontrol syneresis. Excessive addition of stabilizers, however, couldalso make the product too viscous adversely affecting mouthfeel andtaste.

-   Wright and Rand, 1973; J. Food Sci. 38: 1132-1135 discloses    enzymatic conversion of lactose to lactobiotic acid and its use to    acidify milk.-   Lin et al., 1993; Biotech. Adv. 11: 417-427 discloses the use of an    oligosaccharide oxidase to convert lactose to lactobionic acid in a    wheat bran substrate.-   Satory et al., 1997; Biotechnol. Lett. 19:1205-1208 discloses the    use of glucose-fructose oxidoreductase (GFOR) for the conversion of    lactose to lactobionic acid.

None of these references discusses the use of enzymatic conversion oflactose to lactobionic acid for affecting functional and/or organolepticproperties, such as firmness and sourness of a dairy product.

Thus, there is a need for an improved method for the preparation offermented dairy products, in particular a method for providing dairyproducts having improved functional and/or organoleptic properties.

One object of the present invention is to provide a method for thepreparation of a fermented dairy product having improved firmness.Specifically, it is an object to provide a less firm fermented dairyproduct.

Another object of the present invention is to provide a method for thepreparation of a fermented dairy product having improved taste.Specifically, it is an object to provide a less sour fermented dairyproduct.

A still further object of the present invention is to provide a methodfor affecting firmness and sourness of a fermented dairy product.Specifically, it is an object to provide a less firm and less sourfermented dairy product.

SUMMARY OF THE INVENTION

According to the invention it has been found that by the use of anoxidase from Microdochium in the preparation of a fermented dairyproduct it has been possible to affect the firmness and sourness of theresulting product. It has specifically been found that it is therebypossible to produce a less firm and less sour fermented dairy product.

Thus, the present invention relates to a method for the preparation of afermented dairy product comprising the steps of

-   providing a dairy base-   contacting the dairy base with a starter culture for fermentation-   adding to the dairy base, prior to or during fermentation, an    oxidase, produced by a fungus belonging to the genus Microdochium,    for conversion of lactose to lactobionic acid to give a fermented    dairy product.

In a further aspect the invention relates to a method for affectingfirmness of a fermented dairy product comprising the steps of

-   providing a dairy base-   contacting the dairy base with a starter culture for fermentation-   adding to the dairy base, prior to or during fermentation, an    oxidase, produced by a fungus belonging to the genus Microdochium,    for conversion of lactose to lactobionic acid to give a fermented    dairy product.

In yet a further aspect the present invention relates to a method foraffecting firmness and/or sourness of a fermented acidified dairyproduct comprising the steps of

-   providing a dairy base-   contacting the dairy base with a starter culture for fermentation-   adding to the dairy base, prior to or during fermentation, an    oxidase, produced by a fungus belonging to the genus Microdochium,    for conversion of lactose to lactobionic acid to give a fermented    acidified dairy product.

Moreover, the present invention refers to the use of an oxidase,produced by a fungus belonging to the genus Microdochium, in combinationwith fermentation of a dairy base in the production of a fermented dairyproduct for conversion of lactose to lactobionic acid.

Finally, the present invention refers to fermented dairy productsproduced by the above methods.

DETAILED DISCLOSURE OF THE INVENTION

The present invention refers to the preparation of a fermented dairyproduct having improved functional and/or organoleptic properties.Specifically, it refers to the preparation of a fermented dairy producthaving improved firmness and taste.

Dairy Base and the Preparation of a Fermented Dairy Product

In the present context the term “dairy base” is to be understood as anymilk or milk like product including lactose, such as whole or low fatmilk, skim milk, condensed milk, dried skim milk or cream originatingfrom any animal. “Milk” is here to be understood as the lactealsecretion obtained by milking any animal, such as cows, sheep, goats,buffaloes or camels. Also, it is to be understood that the milk or milklike product can be produced by suspending skim milk powder and/or fullfat milk powder in an aqueous medium.

In the present context the term “fermented dairy product” is to beunderstood as any dairy product including a dairy base, as definedabove, and being subjected to any type of fermentation. Examples offermented dairy products applicable for the present invention areproducts like yoghurt, cream cheese and cottage cheese.

For the preparation of a fermented dairy product a dairy base, asdefined above, is provided. The dairy base may be heat treated bypasteurisation, sterilization or treated in any other appropriate way.The pasteurisation and sterilization procedures may be any suchprocedure known in the art. For fermentation the dairy base is contactedwith a starter culture, which is chosen depending on the product to beproduced. Examples of starter cultures to be used according to theinvention are lactic starter cultures, such as yoghurt cultures(Lactobacillus delbrueckii subsp. bulgaricus and Streptococcusthermophilus. Others include Lactobacillus acidophilus, Lactobacilluslactis, and bifidobacteria), cheese cultures (Lactococcus spp.Lactobacillus spp. Streptococcus spp.). Such cultures are readilyavailable from e.g. Chr. Hansen A/S, Denmark. However, any starterculture available within the art and suitable for producing a fermenteddairy product may be used.

Doses of starter culture added and incubation temperatures varydepending e.g. on the culture/dairy base used and the final productrequired. However, culture doses often range between 2-5% inoculatedinto warm homogenized mix and incubated at about 45° C. for about 3-6hrs until pH drops to about 4.4. In some cases, a lower temperature (32°C.) coupled with a lower culture dose of 0.25% may be used with longincubation times (12-14 hrs).

Prior to or during the fermentation the dairy base is subjected to anoxidase produced by a fungus belonging to the genus Microdochium.Preferably the fungus is Microdochium nivale, such as Microdochiumnivale as deposited under the deposition no CBS 100236. Subjecting thedairy base to a Microdochium oxidase results in the conversion oflactose in the dairy base to lactobionic acid.

Doses of enzyme added vary depending on e.g. dairy base used and thespecific product to be produced. Doses of enzyme added may range from4-20 units/100 ml dairy base, a preferred level being about 10 units/100ml dairy base.

The dairy base including the starter culture and the oxidase is allowedto ferment under conditions generally known in the art. Examples offermentation conditions are 40-46° C. for 3-6 hrs until a pH of 4.2-4.6is reached. In some cases, it may be possible to use lower doses ofculture (about 0.25%) and incubation at about 32° C. for as long as12-14 hrs until the desired final pH is reached.

According to the present invention the oxidase is used to affectfunctional and/or organoleptic properties, such as firmness andsourness, of the dairy product to be produced. If necessary, additives,such as stabilizers and sweeteners, may be added to the dairy product.

In a further embodiment of the present invention the oxidase treateddairy base sample is subjected to a heat treatment prior tofermentation. The dairy base is heat treated before the addition ofstarter culture thereto and as an example the heat treatment may beperformed 20-40 min, such as 30 min after the addition of oxidase. Theheat treatment per se may be a treatment of up to about 90° C., such asaround 60-90° C., e.g. 60-75° C., for 35 sec-5 min. One example of heattreatment is 90° C. for 5 min. In one embodiment of the invention theheat treatment is sufficient to inactivate the oxidase enzyme. Oneeffect of this heat treatment is that the lowering of the firmness isless pronounced (as shown by sample no 4 in example 1), whereas theproduct still shows a reduction of the sourness.

Products Produced by the Method of the Invention

The product produced by the present invention may be any fermented dairyproduct, as defined above. Examples of such products are yoghurts, creamcheeses and cottage cheeses, some specific examples of which are furtherdisclosed below.

Flavored and Plain Yoghurts:

Milk mix is pre-heated or concentrated to pasteurisation temperature and0.5% stabilizer added, if required. This is homogenized and pasteurisedat 91° C. for 40-60 sec (HTST) or 85° C. for 30 min. The pasteurised mixis cooled to about 46° C. and after holding for about 15 min at thistemperature; it is inoculated with appropriate dose of culture. Forflavoured products, recommended amounts of essences are added at thispoint, packaged, and incubated at this temperature for about 4-6 hrs oruntil firm smooth gel is formed. At this point, pH should be about 4.5.These are then transferred to 2° C. chill rooms where the fresh yoghurtis rapidly chilled to 7° C. in less than an hour. These are stored at 4°C. for 1-2 months.

Pasteurised or Heated Yoghurt

The freshly prepared yoghurt makes up the basic ingredient for heated orpasteurized yoghurt which is prepared by adding 0.15-0.2% stabilizer(e.g., locust bean gum or alginate). The stabilized product is heated at62° C. or 75° C. for 35 sec for direct hot packaging or cooling prior toaseptic packaging.

Low Lactose Yoghurt

For low lactose yoghurt, lactase is added to milk and held overnight at4° C. until about 60% lactose is hydrolyzed. Lactose reduction issometimes achieved by ultrafiltration of the milk blend or a combinationof ultrafiltration and lactase treatment. The mix is then pasteurizedand incubated at 43° C. with appropriate culture until curd is properlyset. This is then chilled as for plain or flavoured yoghurt.

In all examples mentioned above, the enzyme may be incorporated at theappropriate stages as outlined in the description and the examples.

The yoghurts produced by the method of the present invention compriseall varieties of yoghurts, such as, yoghurt mousse, Acidophilus andBifidus yoghurt, low lactose yoghurt, low fat and non-fat yoghurts,heated or pasteurised yoghurt.

The cheeses produced by the process of the present invention compriseall varieties of cheese, such as, e.g., Manchego, Saint Paulin, Softcheese, White cheese, including rennet-curd cheese produced byrennet-coagulation of the cheese curd; ripened cheeses such as Cheddar,Colby, Camembert, fresh cheeses such as Mozzarella and Feta; acidcoagulated cheeses such as cream cheese, Neufchatel, Quarg, CottageCheese and Queso Blanco; and pasta filata cheese.

Discussion and Further Aspects of the Invention

According to the present invention a fermented dairy product having animproved firmness is provided. Specifically, a fermented dairy producthaving a reduced firmness is provided. One example of such a product isyoghurt and by means of the present invention a softer yoghurt isprovided, which in many cases will be experienced as a product havingbetter mouthfeel than a more firm product.

In another aspect of the invention a fermented acidified dairy producthaving an improved sourness is provided. Specifically, a fermentedacidified dairy product having a reduced sourness is provided. Oneexample of such a product is yoghurt and the characteristic yoghurttaste, specifically related to acetaldehyde, is surprisingly reduced bymeans of the present invention. This is shown in example 2.

In still another aspect of the invention a fermented acidified dairyproduct having an improved firmness is provided. Specifically, afermented acidified dairy product having a reduced firmness is provided.

Thus, it is, by means of the invention, possible to affect the firmnessand/or sourness of a fermented dairy product and in a preferredembodiment the dairy product produced by means of the invention has afirmness and/or a sourness which is lower than the firmness and/orsourness achieved in such a product without the addition of oxidase. Ina further embodiment of the present invention the oxidase treated dairybase, as described above, is heat treated before the addition of astarter culture. This results, as shown in example 1, no 4, in a productwhere the lowering of the firmness is less pronounced. However, theproduct still have a less sour taste.

A further aspect of the invention is the use of an oxidase, produced bya fungus belonging to the genus Microdochium, in combination withfermentation of a dairy base in the production of a fermented dairyproduct for conversion of lactose to lactobionic acid.

Preferably the fungus is Microdochium nivale, such as Microdochiumnivale as deposited under the deposition no CBS 100236 or any otherspecies as defined above.

Further aspects of the invention are fermented dairy products producedby the method according to the invention. The products of the inventionhave improved functional and/or organoleptic properties, such asimproved firmness and sourness. Specifically there is provided afermented dairy product having a firmness being lower than the firmnessachieved in such a product without the addition of an oxidase.

In a further embodiment a fermented acidified dairy product is providedhaving a sourness being lower than the sourness achieved without theaddition of an oxidase.

In still a further embodiment a fermented acidified dairy product isprovided having a firmness as well as a sourness being lower than thefirmness and sourness achieved in such a product without the addition ofan oxidase.

The present invention is further illustrated in the following examples,which are not to be in any way limiting the scope of protection.

EXAMPLES

For the determination of the oxidase effect on firmness and sourness ofa fermented dairy product, such as a yoghurt culture, the followingexamples were performed. Materials and procedure used were as statedbelow.

Materials:

Culture prep.: DVS Thermophilic Lactic Culture, YC-350 (K) Package 50-U,Batch 5007571, a yoghurt culture from Chr. Hansen, Denmark

-   -   50 units diluted in 250 ml water    -   10 ml added/approx 180 ml milk

Enzyme prep: Microdochium nivale CBS 100236 (no 00720 MCO), 10 units/100ml milk (For the definition of units reference is made to WO 99/31990).

The following milk samples were prepared:

-   1 Starter culture-   2 Enz. no. 00720 MCO-   3 Starter culture+enz. no. 00720 MCO-   4 Enz. no. 00720 MCO, heat treated after 30 min at 40° C., then    addition of culture    Procedure:

A yoghurt was produced whereto enzyme was added during the fermentation.Firmness and taste evaluations were done and the achieved results arereported in examples 1 and 2, respectively. Full fat milk was heattreated at 90° C. for 5 min, tempered to approx. 40° C. and the aboveenzyme and/or culture was added. The samples were allowed to ferment at40° C. until pH 4.2 was reached. After 30 min enzyme reaction at 40° C.sample no. 4 was heat treated for 5 min. at 90° C.

Example 1

Example 1 shows the effect of oxidase treatment on yoghurt firmness,comparing oxidase treated yoghurt with non-oxidase treated yoghurt.

Results:

TPA (Texture Profile Analysis) was tested on a TA-XT2 Texture Analyser(Texture Technologies Corp, Scarsdale, NY).

Parameters: 20 mm probe; 20% deformation; 2 sec. rest between eachprofile; 2 mm/sec pre test speed; 5 mm/sec post test speed TABLE 1Firmness (max force measured, N) Sample Test 1 Test 2 Standard no.Firmness Firmness Average deviation Starter culture 1 0.68 0.692 0.6860.008 enz. no. 00720 2 0 0 0.000 0.000 MCO Starter culture + 3 0.4590.456 0.458 0.002 enz. no. 00720 MCO enz. no. 00720 4 0.639 0.579 0.6090.042 MCO heat treated after 30 min at 40° C. Then addition of cultureDiscussion:

The enzyme treated sample no 3 shows a substantially lower firmness thansample no 1, not being enzyme treated. Also sample no 4, where theenzyme has been heat treated before culture addition shows asignificantly lower firmness than sample nol. The enzyme treated yoghurtno 3, though softer than the control, is able to hold its shape sinceTPA analysis requires the sample to have some defined shape.

Example 2

Example 2 shows the effect of oxidase treatment on yoghurt taste,comparing oxidase treated yoghurt with non-oxidase treated yoghurt.

Taste evaluations:

3 judges evaluated the 3 cooled yoghurts at day 7. TABLE 2 Commentssample no. Judge 1 2 3 Judges 1-3 Sour liquid Less sour than no. 1.acetaldehyde Blue/sour smellDiscussion:

The characteristic yoghurt taste (acetaldehyde) was less pronounced inthe enzyme treated sample no 3.

1-17. (canceled)
 18. A method for preparing a cheese product, comprisinga) providing a dairy base; and b) fermenting the dairy base with astarter culture to produce a cheese product; wherein prior to or duringfermentation, adding to the dairy base an oxidase produced by a fungusbelonging to the genus Microdochium.
 19. The method of claim 18, whereinthe cheese product is a fermented acidified cheese product.
 20. Themethod of claim 18, wherein the cheese product has improved firmness ascompared to a cheese product which was produced without the addition ofthe oxidase.
 21. The method of claim 18, wherein the cheese product is afermented acidified cheese product, and wherein the cheese product hasimproved firmness and/sourness as compared to a fermented acidifiedcheese product which was produced without the addition of the oxidase.22. The method of claim 18, wherein the fungus is Microdochium nivale.23. The method of claim 18, wherein the fungus is Microdochium nivaleCBS
 100236. 24. The method of claim 18, further comprising the step ofheat treating the dairy base after the addition of oxidase, but prior toadding a starter culture for fermenting the dairy base.
 25. The methodof claim 18, wherein the starter culture is a lactic starter culture.